Liquid-crystalline medium

ABSTRACT

A liquid-crystalline medium based on a mixture of polar compounds of positive dielectric anisotropy, which contains one or more compounds of the formula I  
                 
 
     and one or more compounds of the formula IA  
                 
 
     in which R 1 , R 2 , ring A, L 1-8 , Z 1 , X 1  and X 2  are as defined in claim 1.

[0001] The present invention relates to a liquid-crystalline medium, tothe use thereof for electro-optical purposes, and to displays containingthis medium.

[0002] Liquid crystals are used principally as dielectrics in displaydevices, since the optical properties of such substances can be modifiedby an applied voltage. Electro-optical devices based on liquid crystalsare extremely well known to the person skilled in the art and can bebased on various effects. Examples of such devices are cells havingdynamic scattering, DAP (deformation of aligned phases) cells,guest/host cells, TN cells having a twisted nematic structure, STN(supertwisted nematic) cells, SBE (superbirefringence effect) cells andOMI (optical mode interference) cells. The most common display devicesare based on the Schadt-Helfrich effect and have a twisted nematicstructure.

[0003] The liquid-crystal materials must have good chemical and thermalstability and good stability to electric fields and electromagneticradiation. Furthermore, the liquid-crystal materials should have lowviscosity and produce short addressing times, low threshold voltages andhigh contrast in the cells.

[0004] They should furthermore have a suitable mesophase, for example anematic or cholesteric mesophase for the above-mentioned cells, at theusual operating temperatures, i.e. in the broadest possible range aboveand below room temperature. Since liquid crystals are generally used asmixtures of a plurality of components, it is important that thecomponents are readily miscible with one another. Further properties,such as the electrical conductivity, the dielectric anisotropy and theoptical anisotropy, have to satisfy various requirements depending onthe cell type and area of application. For example, materials for cellshaving a twisted nematic structure should have positive dielectricanisotropy and low electrical conductivity.

[0005] For example, for matrix liquid-crystal displays with integratednon-linear elements for switching individual pixels (MLC displays),media having large positive dielectric anisotropy, broad nematic phases,relatively low birefringence, very high specific resistance, good UV andtemperature stability and lower vapor pressure are desired.

[0006] Matrix liquid-crystal displays of this type are known. Non-linearelements which can be used for individual switching of the individualpixels are, for example, active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made betweentwo types:

[0007] 1. MOS (metal oxide semiconductor) or other diodes on a siliconwafer as substrate.

[0008] 2. Thin-film transistors (TFTs) on a glass plate as substrate.

[0009] The use of single-crystal silicon as substrate material restrictsthe display size, since even modular assembly of various part-displaysresults in problems at the joins.

[0010] In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect. A distinction ismade between two technologies: TFTs comprising compound semiconductors,such as, for example, CdSe, or TFTs based on polycrystalline oramorphous silicon. Intensive work is being carried out world-wide on thelatter technology.

[0011] The TFT matrix is applied to the inside of one glass plate of thedisplay, while the other glass plate carries the transparentcounterelectrode on its inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fully color-capabledisplays, in which a mosaic of red, green and blue filters is arrangedin such a way that a filter element is opposite each switchable pixel.

[0012] The TFT displays usually operate as TN cells with crossedpolarizers in transmission and are illuminated from the back.

[0013] The term MLC displays here covers any matrix display withintegrated non-linear elements, i.e., besides the active matrix, alsodisplays with passive elements, such as varistors or diodes(MIM=metal-insulator-metal).

[0014] MLC displays of this type are particularly suitable for TVapplications (for example pocket TVs) or for high-information displaysfor computer applications (laptops) and in automobile or aircraftconstruction. Besides problems regarding the angle dependence of thecontrast and the response times, difficulties also arise in MLC displaysdue to insufficiently high specific resistance of the liquid-crystalmixtures [TOGASHI, S., SEKOGUCHI, K., TANABE, H., YAMAMOTO, E.,SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay84, September 1984: A 210-288 Matrix LCD Controlled by Double StageDiode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84,September 1984: Design of Thin Film Transistors for Matrix Addressing ofTelevision Liquid Crystal Displays, p. 145 ff, Paris]. With decreasingresistance, the contrast of an MLC display deteriorates, and the problemof after-image elimination may occur. Since the specific resistance ofthe liquid-crystal mixture generally drops over the life of an MLCdisplay owing to interaction with the interior surfaces of the display,a high (initial) resistance is very important in order to obtainacceptable service lives. In particular in the case of low-voltmixtures, it was hitherto impossible to achieve very high specificresistance values. It is furthermore important that the specificresistance exhibits the smallest possible increase with increasingtemperature and after heating and/or UV exposure. The low-temperatureproperties of the mixtures from the prior art are also particularlydisadvantageous. It is demanded that no crystallization and/or smecticphases occur, even at low temperatures, and the temperature dependenceof the viscosity is as low as possible. The MLC displays from the priorart thus do not meet today's requirements.

[0015] There thus continues to be a great demand for MLC displays havingvery high specific resistance at the same time as a largeworking-temperature range, short response times even at low temperaturesand a low threshold voltage which do not have these disadvantages, oronly do so to a reduced extent.

[0016] In addition to liquid-crystal displays which use back-lighting,i.e. are operated transmissively and if desired transflectively,reflective liquid-crystal displays are also particularly interesting.These reflective liquid-crystal displays use the ambient light forinformation display. They thus consume significantly less energy thanback-lit liquid-crystal displays having a corresponding size andresolution. Since the TN effect is characterized by very good contrast,reflective displays of this type can even be read well in bright ambientconditions. This is already known of simple reflective TN displays, asused, for example, in watches and pocket calculators. However, theprinciple can also be applied to high-quality, higher-resolution activematrix-addressed displays, such as, for example, TFT displays. Here, asalready in the transmissive TFT-TN displays which are generallyconventional, the use of liquid crystals of low birefringence (Δn) isnecessary in order to achieve low optical retardation (d·Δn). This lowoptical retardation results in usually acceptable low viewing-angledependence of the contrast (cf. DE 30 22 818). In reflective displays,the use of liquid crystals of low birefringence is even more importantthan in transmissive displays since the effective layer thicknessthrough which the light passes is approximately twice as large inreflective displays as in transmissive displays having the same layerthickness.

[0017] In TN (Schadt-Helfrich) cells, media are desired which facilitatethe following advantages in the cells:

[0018] extended nematic phase range (in particular down to lowtemperatures)

[0019] storage stability, even at extremely low temperatures

[0020] the ability to switch at extremely low temperatures (outdoor use,automobiles, avionics)

[0021] increased resistance to UV radiation (longer service life)

[0022] low optical birefringence (Δn) for reflective displays.

[0023] The media available from the prior art do not allow theseadvantages to be achieved while simultaneously retaining the otherparameters.

[0024] In the case of supertwisted (STN) cells, media are desired whichenable greater multiplexability and/or a lower threshold voltage and/orbroader nematic phase ranges (in particular at low temperatures). Tothis end, a further widening of the available parameter latitude(clearing point, smectic-nematic transition or melting point, viscosity,dielectric para-meters, elastic parameters) is urgently desired.

[0025] The invention has an object of providing media, in particular forMLC, TN or STN displays of this type, which do not have theabove-mentioned disadvantages or only do so to a reduced extent, andpreferably simultaneously have very low threshold voltages and at thesame time high values for the voltage holding ratio (VHR).

[0026] Upon further study of the specification and appended claims,further objects and advantages of this invention will become apparent tothose skilled in the art.

[0027] It has now been found that these and other objects can beachieved if media according to the invention are used in displays.

[0028] The invention thus relates to a liquid-crystalline medium basedon a mixture of polar compounds of positive dielectric anisotropy,characterized in that it comprises one or more compounds of the formulaI

[0029] and one or more compounds of the formula IA

[0030] in which the individual radicals have the following meanings:

[0031] R¹ and R² are each, independently of one another, H, ahalogenated or unsubstituted alkyl radical having from 1 to 15 carbonatoms, where one or more CH₂ groups in these radicals may also bereplaced, in each case independently of one another, by —C≡C—, —CH═CH—,—O—,

[0032]  —CO—O— or —O—CO— in such a way that O atoms are not linkeddirectly to one another,

[0033] X¹ and X² are each, independently of one another, F, Cl, CN, SF₅,SCN, NCS, or OCN, or a halogenated alkyl radical, a halogenated alkenylradical, a halogenated alkoxy radical or a halogenated alkenyloxyradical, each having 1 to 6 carbon atoms,

[0034] z¹ is —CH₂CH₂—, —CH═CH—, —C≡C—, —COO—, —CH₂O—, —OCH₂—, —OOC—,—(CH₂)₄—, —HFO—, —CH═CF—, —CF═CH—, —CF═CF—, —C₂F₄—, —CF₂O—, —OCF₂— or asingle bond,

[0035] L¹⁻⁸ are each, independently of one another, H or F.

[0036] The compounds of the formulae I and IA have a broad range ofapplications. Depending on the choice of substituents, these compoundscan serve as base materials of which liquid-crystalline media arepredominantly composed; however, it is also possible to add compounds ofthe formulae I and IA to liquid-crystalline base materials from otherclasses of compound in order, for example, to modify the dielectricand/or optical anisotropy of a dielectric of this type and/or in orderto optimize its threshold voltage and/or its viscosity. The mixingconcept according to the invention results in mixtures which aredistinguished over the prior art, for example, by their very goodreliability and V_(th)/γ₁ ratio, in particular in 2.5 V and 3.3 Vmixtures. Furthermore, the mixtures according to the invention aredistinguished over the prior art, such as, for example, EP 10 46 693 andEP 10 46 694, by smaller values for the birefringence. The mixturesaccording to the invention preferably have Δn values of <0.0780.

[0037] In the pure state, the compounds of the formulae I and IA arecolorless and form liquid-crystalline mesophases in a temperature rangewhich is favorably located for electro-optical use. They are stablechemically, thermally and to light.

[0038] Preferred radicals for the compounds of the formulae I and IA areindicated below.

[0039] X¹ and X² in the compounds of the formulae are, independently ofone another, preferably F, Cl, CN, NCS, CF₃, C₂F₅, C₃F₇, SF₅, CF₂H,OCF₃, OCF₂H, OCFHCF₃, OCFHCFH₂, OCFHCF₂H, OCF₂CH₃, OCF₂CFH₂, OCF₂CF₂H,OCF₂CF₂CF₂H, OCF₂CF₂CFH₂, OCFHCF₂CF₃, OCFHCF₂CF₂H, OCFHCFHCF₃,OCH₂CF₂CF₃, OCF₂CF₂CF₃, OCF₂CFHCFH₂, OCF₂CH₂CF₂H, OCFHCF₂CFH₂,OCFHCFHCF₂H, OCFHCH₂CF₃, OCH₂CFHCF₃, OCH₂CF₂CF₂H, OCF₂CFHCH₃,OCF₂CH₂CFH₂, OCFHCF₂CH₃, OCFHCFHCFH₂, OCFHCH₂CF₃, OCH₂CF₂CFH₂,OCH₂CFHCF₂H, OCF₂CH₂CH₃, OCFHCFHCH₃, OCFHCH₂CFH₂, OCH₂CF₂CH₃,OCH₂CFHCFH₂, OCH₂CH₂CF₂H, OCHFCH₂CH₃, OCH₂CFHCH₃, OCH₂CH₂CF₂H, OCCIFCF₃,OCCIFCClF₂, OCCIFCFH₂, OCFHCCl₂F, OCClFCF₂H, OCClFCClF₂, OCF₂CClH₂,OCF₂CCl₂H, OCF₂CCl₂F, OCF₂CClFH, OCF₂CClF₂, OCF₂CF₂CClF₂, OCF₂CF₂CCl₂F,OCClFCF₂CF₃, OCClFCF₂CF₂H, OCClFCF₂CClF₂, OCClFCFHCF₃, OCClFCClFCF₃,OCCl₂CF₂CF₃, OCClHCF₂CF₃, OCClFCF₂CF₃, OCClFCClFCF₃, OCF₂CClFCFH₂,OCF₂CF₂CCl₂F, OCF₂CCl₂CF₂H, OCF₂CH₂CClF₂, OCClFCF₂CFH₂, OCFHCF₂CCl₂F,OCClFCFHCF₂H, OCClFCClFCF₂H, OCFHCFHCClF₂, OCClFCH₂CF₃, OCFHCCl₂CF₃,OCCl₂CFHCF₃, OCH₂CClFCF₃, OCCl₂CF₂CF₂H, OCH₂CF₂CClF₂, OCF₂CClFCH₃,OCF₂CFHCCl₂H, OCF₂CCl₂CFH₂, OCF₂CH₂CCl₂F, OCClFCF₂CH₃, OCFHCF₂CCl₂H,OCClFCClFCFH₂, OCFHCFHCCl₂F, OCClFCH₂CF₃, OCFHCCl₂CF₃, OCCl₂CF₂CFH₂,OCH₂CF₂CCl₂F, OCCl₂CFHCF₂H, OCClHCClFCF₂H, OCF₂CClHCClH₂, OCF₂CH₂CCl₂H,OCClFCFHCH₃, OCF₂CClFCCl₂H, OCClFCH₂CFH₂, OCFHCCl₂CFH₂, OCCl₂CF₂CH₃,OCH₂CF₂CClH₂, OCCl₂CFHCFH₂, OCH₂CClFCFCl₂, OCH₂CH₂CF₂H, OCClHCClHCF₂H,OCH₂CCl₂CF₂H, OCClFCH₂CH₃, OCFHCH₂CCl₂H, OCClHCFHCClH₂, OCH₂CFHCCl₂H,OCCl₂CH₂CF₂H, OCH₂CCl₂CF₂H, CH═CF₂, CF═CF₂, OCH═CF₂, OCF═CF₂, CH═CHF,OCH═CHF, CF═CHF, OCF═CHF, in particular F, Cl, CN, NCS, CF₃, SF₅, CF₂H,OCF₃, OCF₂H, OCFHCF₃, OCFHCFH₂, OCFHCF₂H, OCF₂CH₃, OCF₂CFH₂, OCF₂CF₂H,OCF₂CF₂CF₂H, OCF₂CF₂CFH₂, OCFHCF₂CF₃, OCFHCF₂CF₂H, OCF₂CF₂CF₃ orOCF₂CHFCF₃.

[0040] If R¹ and/or R² are an alkyl radical and/or an alkoxy radical,this may be straight-chain or branched. It is preferably straight-chain,has 1, 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly is preferablymethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy,butoxy, pentoxy, hexyloxy or heptyloxy, furthermore octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy,nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy ortetradecyloxy.

[0041] Oxaalkyl is preferably straight-chain 2-oxapropyl(=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-,3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0042] If R¹ and/or R² are an alkyl radical in which one CH₂ group hasbeen replaced by —CH═CH—, this may be straight-chain or branched. It ispreferably straight-chain and has from 2 to 10 carbon atoms.Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2-or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or-5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-,-5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, ordec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

[0043] If R¹ and/or R² are an alkyl radical in which one CH₂ group hasbeen replaced by —O— and one has been replaced by —CO—, these arepreferably adjacent. These thus contain an acyloxy group —CO—O— or anoxycarbonyl group —O—CO—. These are preferably straight-chain and havefrom 2 to 6 carbon atoms. Accordingly, they are in particular acetoxy,propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl,propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl,2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 2-acetoxypropyl,3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl,methoxycarbonyl-methyl, ethoxycarbonylmethyl, propoxycarbonylmethyl,butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0044] If R¹ and/or R² are an alkyl radical in which one CH₂ group hasbeen replaced by unsubstituted or substituted —CH═CH— and an adjacentCH₂ group has been replaced by CO or CO—O or O—CO, this may bestraight-chain or branched. It is preferably straight-chain and has from4 to 12 carbon atoms. Accordingly, it is in particularacryloyloxymethyl, 2-acryl-oyloxyethyl, 3-acryloyloxypropyl,4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxy-hexyl,7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl,10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl,3-methacryloyloxypropyl, 4-methacryloyloxybutyl,5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or9-methacryloyloxynonyl.

[0045] If R¹ and/or R² are an alkyl or alkenyl radical which ismonosubstituted by CN or CF₃, this radical is preferably straight-chain.The substitution by CN or CF₃ is in any desired position.

[0046] If R¹ and/or R² are an alkyl or alkenyl radical which is at leastmonosubstituted by halogen, this radical is preferably straight-chain,and halogen is preferably F or Cl. In the case of polysubstitution,halogen is preferably F. The resultant radicals also includeperfluorinated radicals. In the case of monosubstitution, the fluorineor chlorine substituent may be in any desired position, but ispreferably in the co-position.

[0047] Compounds containing branched wing groups R¹ and/or R mayoccasionally be of importance owing to better solubility in theconventional liquid-crystalline base materials, but in particular aschiral dopants if they are optically active. Smectic compounds of thistype are suitable as components of ferroelectric materials.

[0048] Branched groups of this type generally contain not more than onechain branch. Preferred branched radicals R are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexyloxy,1-methylhexyloxy and 1 -methylheptyloxy.

[0049] If R¹ and/or R² are an alkyl radical in which two or more CH₂groups have been replaced by —O— and/or —CO—O—, this may bestraight-chain or branched. It is preferably branched and has from 3 to12 carbon atoms. Accordingly, it is in particular biscarboxymethyl,2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl,5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl,8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl,bis(methoxycarbonyl)methyl, 2,2-bis(methoxy-carbonyl)ethyl,3,3-bis(methoxycarbonyl)propyl, 4,4-bis(methoxycarbonyl)butyl,5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl,7,7-bis-(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl,bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl,3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl or5,5-bis(ethoxycarbonyl)pentyl.

[0050] Z¹ is preferably a single bond, furthermore —C₂F₄—, —COO—, —C₂H₄—or —CF₂O—.

[0051] Ring A is preferably

[0052] furthermore

[0053] The compounds of the formulae I and IA can be prepared by methodsknown per se, as described in the literature (for example in thestandard works, such as Houben-Weyl, Methoden der organischen Chemie[Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to beprecise under reaction conditions which are known and suitable for thesaid reactions. Use can also be made here of variants which are knownper se, but are not mentioned here in greater detail. The compounds ofthe formula IA are known, for example, from EP 1 046 693 A1 and EP 1 046694 A1. The compounds of the formula I are described, for example, in GB2,229,438.

[0054] The invention also relates to electro-optical displays (inparticular STN or MLC displays having two plane-parallel outer plates,which, together with a frame, form a cell, integrated non-linearelements for switching individual pixels on the outer plates, and anematic liquid-crystal mixture of positive dielectric anisotropy andhigh specific resistance which is located in the cell) which containmedia of this type, and to the use of these media for electro-opticalpurposes.

[0055] The liquid-crystal mixtures according to the invention enable asignificant widening of the available parameter latitude. The achievablecombinations of clearing point, viscosity at low temperature, thermaland UV stability and dielectric anisotropy are far superior to previousmaterials from the prior art.

[0056] Compared with the mixtures disclosed in EP 1 046 693 A1, themixtures according to the invention have low y, values and relativelylow threshold and An values. The mixtures according to the invention arepreferably suitable as TN-TFT mixtures for notebook PC applications with3.3 and 2.5 V drivers.

[0057] The liquid-crystal mixtures according to the invention, whilepreferably retaining the nematic phase down to −30° C., particularlypreferably down to −40° C., enable clearing points preferably above 70°C., more preferably above 75° C., particularly preferably above 80° C.,simultaneously dielectric anisotropy values, Δε, preferably of ≧6, morepreferably ≧8, and a high value for the specific resistance to beachieved, enabling excellent STN and MLC displays to be obtained. Inparticular, the mixtures are characterized by low operating voltages.The TN thresholds are preferably below 1.5 V, more preferably below 1.4V, particularly preferably <1.3 V.

[0058] It goes without saying that, through a suitable choice of thecomponents of the mixtures according to the invention, it is alsopossible for higher clearing points (for example above 110° C.) to beachieved at higher threshold voltages or lower clearing points to beachieved at lower threshold voltages with retention of the otheradvantageous properties. At viscosities correspondingly increased onlyslightly, it is likewise possible to obtain mixtures having greater Δεand thus low thresholds. The MLC displays according to the inventionpreferably operate at the first Gooch and Tarry transmission minimum [C.H. Gooch and H. A. Tarry, Electron. Lett. 10, 2-4, 1974; C. H. Gooch andH. A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], where, besidesparticularly favorable electro-optical properties, such as, for example,high steepness of the characteristic line and low angle dependence ofthe contrast (German Patent 30 22 818), a lower dielectric anisotropy issufficient at the same threshold voltage as in an analogous display atthe second minimum. This enables significantly higher specificresistances to be achieved using the mixtures according to the inventionat the first minimum than in the case of mixtures comprising cyanocompounds. Through a suitable choice of the individual components andtheir proportions by weight, the person skilled in the art is able toset the birefringence necessary for a pre-specified layer thickness ofthe MLC display using simple routine methods.

[0059] The flow viscosity ν₂₀ at 20° C. is preferably <60 mm²·s⁻¹,particularly preferably <50 mm²·s⁻¹. The rotational viscosity γ₁ at 20°C. of the mixtures according to the invention is preferably <140 mPa·s,particularly preferably <120 mPa.s. The nematic phase range ispreferably at least 100° , in particular at least 110°. This rangepreferably extends at least from −40° to +80°.

[0060] A short response time is desired in liquid-crystal displays. Thisapplies in particular to displays which are capable of videoreproduction. For displays of this type, response times (sum:t_(on)+t_(off)) of at most 16 ms are required. The upper limit of theresponse time is determined by the image refresh frequency.

[0061] Measurements of the voltage holding ratio (HR) [S. Matsumoto etal., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SIDConference, San Francisco, June 1984, p. 304 (1984); G. Weber et al.,Liquid Crystals 5, 1381 (1989)] have shown that mixtures according tothe invention comprising compounds of the formulae I and IA exhibit asignificantly smaller decrease in the HR with increasing temperaturethan analogous mixtures comprising cyanophenylcyclohexanes of theformula

[0062] or esters of the formula

[0063] instead of the compounds of the formula IA.

[0064] The mixtures according to the invention preferably comprise onlysmall amounts (≦10% by weight) or no nitrites. The mixtures according tothe invention have values for the holding ratio of >98%, in particulargreater than 99%.

[0065] The UV stability of the mixtures according to the invention isalso considerably better, i.e. they exhibit a significantly smallerdecrease in the HR on exposure to UV.

[0066] The formula I compounds preferably are compounds of thesub-formulae I-1 to I-27:

[0067] in which R¹ is as defined above. R¹ is preferably H, CH₃, C₂H₅,n-C₃H₇, n-C₄H₉, n-C₅H₁₁, n-C₆H₁₃, CH₂═CH, CH₃CH═CH, CH₃CH═CHCH₂CH₂ orCH₂═CHCH₂CH₂.

[0068] Preference is given to media according to the invention whichcomprise at least one compound of the formulae I-10 and/or I-19,particularly preferably in each case at least one compound of theformula I-19. Preference is furthermore given to compounds of theformulae I-11 and I-20.

[0069] Particularly preferred compounds of the formula IA are compoundsof the formula IAA:

[0070] In the compound IAA, Z¹ is preferably a single bond.

[0071] Preferred sub-formulae of the formula IA are compounds of thesub-formulae IA-1 to IA-108:

[0072] in which R² is as defined above.

[0073] Of these preferred compounds, particular preference is given tothose of the formulae IA-1 to IA-36, in particular those of the formulaeIA-2, IA-3, IA-5, IA-6 and IA-14, IA-15 and IA-18, in more particularthose of the formulae IA-3 and IA-15.

[0074] R² in the compounds of the formulae IA and IA-1 to IA-108 ispreferably H, straight-chain alkyl having from 1 to 7 carbon atoms, inparticular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, n-C₆H₁₃, n-C₇H₁₅,furthermore 1E- or 3-alkenyl, in particular CH₂═CH, CH₃CH═CH,CH₂═CHCH₂CH₂ or CH₃CH═CH—CH₂CH₂.

[0075] Preferred embodiments are indicated below:

[0076] The medium comprises one, two or more compounds selected from thegroup consisting of the formulae IA-1 to IA-108;

[0077] The medium preferably comprises in each case one or more,preferably two or three, compounds (homologues) of the formulae I-10and/or I-19;

[0078] The medium preferably comprises in each case one or more,preferably two or three, compounds (homologues) of the formula IA-3;

[0079] The medium additionally comprises one or more compounds selectedfrom the group consisting of compounds of the general formulae II to VI:

[0080] in which the individual radicals have the following meanings:

[0081] R⁰ is n-alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl, eachhaving 1 to 9 carbon atoms,

[0082] X⁰ is F, Cl halogenated alkyl, halogenated alkenyl, halogenatedalkenyloxy or alkoxy having 1 to 6 carbon atoms,

[0083] Z⁰ is —C₂F₄—, —CF═CF—, —CH═CF—, —CF═CH—, —C₂H₄—, —(CH₂)₄—,—OCHF—, —CHFO—, —CH═CH—, —O—CO—, —CF₂O—, —OCF₂—, —OCH₂— or —CH₂O—,

[0084] Y¹ and Y² are each, independently of one another, H or F,

[0085] r is 0 or 1,

[0086] where the compound of the formula VI is not identical with thecompound of formula I.

[0087] The compound of the formula IV is preferably

[0088] The medium additionally comprises one or more compounds selectedfrom the group consisting of the general formulae VII to XII:

[0089] in which R⁰, X⁰, Y¹ and Y² are each, independently of oneanother, as defined above. Y³ and Y⁴ are each, independently of oneanother, H or F. X⁰ is preferably F, Cl, CF₃, OCF₃ or OCHF₂. R⁰ ispreferably alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl, each having1 to 6 carbon atoms.

[0090] The medium additionally comprises one or more ester compounds ofthe formulae Ea to Ef:

[0091] in which R⁰ is as defined above;

[0092] The medium comprises one or more compounds containing a dioxanering, of the formulae D1 and/or D2:

[0093] in which R⁰ and X⁰ are as defined above. X⁰ is preferably F orOCF₃, R⁰ is preferably alkyl.

[0094] The proportion of the compounds of the formulae Ea to Ef ispreferably 10-30% by weight, in particular 15-25% by weight;

[0095] The proportion of compounds of the formulae IA and I to VItogether in the mixture as a whole is at least 50% by weight;

[0096] The proportion of compounds of the formula I in the mixture as awhole is from 5 to 40% by weight, particularly preferably from 10 to 30%by weight;

[0097] The proportion of compounds of the formula IA in the mixture as awhole is from 5 to 40% by weight, particularly preferably from 10 to 30%by weight;

[0098] The proportion of compounds of the formulae II to VI in themixture as a whole is from 30 to 80% by weight;

[0099] The medium comprises compounds of the formula II, IV, I, V or VI;

[0100] R⁰ is straight-chain alkyl or alkenyl having from 2 to 7 carbonatoms;

[0101] The medium essentially consists of compounds of the formulae IAand I and one or more compounds selected from the group consisting ofthe compounds II to VI, where “essentially” denotes ≧60% by weight;

[0102] The medium comprises further compounds, preferably selected fromthe following group consisting of the general formulae XIII to XVI:

[0103] in which R⁰ and X⁰ are as defined above, and the 1,4-phenylenerings may be substituted by CN, chlorine or fluorine. The 1,4-phenylenerings are preferably monosubstituted or polysubstituted by fluorineatoms.

[0104] The medium additionally comprises one or more compounds of theformulae XVII and/or XVIII

[0105] in which R⁰, X⁰, Y¹ and Y² are as defined above.

[0106] The proportion of the compounds of the formulae XVII and/or XVIIIis preferably 2-30% by weight;

[0107] The medium additionally comprises one, two, three or more,preferably two or three, compounds of the formulae

[0108] in which “alkyl” and “alkyl*” are each, independently of oneanother, a straight-chain or branched alkyl radical having 1-9 carbonatoms.

[0109] The proportion of the compounds of the formulae O1 and/or O2 inthe mixtures according to the invention is preferably 5-10% by weight.

[0110] The medium preferably comprises 5-35% by weight of compound IVaand/or IVf.

[0111] The medium preferably comprises one, two or three compounds ofthe formula IVa in which X⁰ is F or OCF₃.

[0112] The medium preferably comprises one or more compounds of theformulae IIa to IIg

[0113] in which R⁰ is as defined above. In the compounds of the formulaeIIa-IIg, R⁰ is preferably H, methyl, ethyl, n-propyl, n-butyl orn-pentyl, furthermore n-hexyl or n-heptyl.

[0114] The (I+IA):(II+III+IV+V+VI) weight ratio is preferably from 1:10to 10:1.

[0115] The medium consists of ≧60% by weight of compounds selected fromthe group consisting of the general formulae IA and I to XVIII.

[0116] The proportion of the compounds of the formulae IVb and/or IVc inwhich X⁰ is fluorine and R⁰ is C₂H₅, n-C₃H₇, n-C₄H₉ or n-C₅H₁₁ in themixture as a whole is from 2 to 20% by weight, in particular from 2 to15% by weight;

[0117] The medium preferably comprises one, two or three, furthermorefour, homologues of the compounds selected from the group consisting ofH1 to H18 (n=1-12):

[0118] The medium preferably comprises the compound IIb in which R⁰ ismethyl;

[0119] The medium comprises further compounds, preferably selected fromthe following group consisting of the formulae RI to RIX:

[0120] in which

[0121] R⁰ is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyloxy oralkenyl, each having up to 9 carbon atoms,

[0122] Y¹ is H or F,

[0123] alkyl and

[0124] alkyl* are each, independently of one another, a straight-chainor branched alkyl radical having 1-9 carbon atoms,

[0125] alkenyl and

[0126] alkenyl* are each, independently of one another, a straight-chainor branched alkenyl radical having from 2 to 9 carbon atoms.

[0127] The proportion of compounds of the formulae RI to RVIII in themixtures according to the invention is preferably from 1 to 40% byweight.

[0128] The medium preferably comprises one or more compounds of theformulae

[0129] in which

[0130] n and m are each 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. n and mare preferably 1, 2, 3, 4, 5 or 6.

[0131] The medium additionally comprises one, two or more compoundscontaining fused rings, of the formulae AN1 to AN12:

[0132] in which R⁰ is as defined above.

[0133] The term “alkyl” or “alkyl*” covers straight-chain and branchedalkyl groups having 1-7 carbon atoms, in particular the straight-chaingroups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groupshaving 2-5 carbon atoms are generally preferred.

[0134] The term “alkenyl” covers straight-chain and branched alkenylgroups having 2-7 carbon atoms, in particular the straight-chain groups.Preferred alkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl,C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particularC₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples ofparticular preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl,1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl,3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl,4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5carbon atoms are generally preferred.

[0135] The term “fluoroalkyl” preferably covers straight-chain groupshaving a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and7-fluoroheptyl. However, other positions of the fluorine are notexcluded.

[0136] The term “alkoxy” or “oxaalkyl” preferably covers straight-chainradicals of the formula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and m areeach, independently of one another, from 1 to 6. Preferably, n=1 and mis from 1 to 6. m may also be 0.

[0137] It has been found that even a relatively small proportion ofcompounds of the formulae I and IA mixed with conventionalliquid-crystal materials, but in particular with one or more compoundsof the formulae II, III, IV, V and/or VI, results in a significantlowering of the threshold voltage and in high values for the VHR (100°C.), with broad nematic phases with low smectic-nematic transitiontemperatures being observed at the same time, improving the shelf life.Preference is given, in particular, to mixtures which, besides one ormore compounds of the formulae I and IA, comprise one or more compoundsof the formula II, in particular compounds of the formula II in which X⁰is F or OCF₃. The compounds of the formulae IA and I to VI arecolorless, stable and readily miscible with one another and with otherliquid-crystal materials.

[0138] Through a suitable choice of the meanings of R⁰ and X⁰, theaddressing times, the threshold voltage, the steepness of thetransmission characteristic lines, etc., can be modified in the desiredmanner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals,2E-alkenyloxy radicals and the like generally result in shorteraddressing times, improved nematic tendencies and a higher ratio betweenthe elastic constants k₃₃ (bend) and k₁₁ (splay) compared with alkyl andalkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the likegenerally give lower threshold voltages and smaller values of k₃₃/k₁₁compared with alkyl and alkoxy radicals.

[0139] A —CH₂CH₂— group generally results in higher values of k₃₃/k₁₁compared with a single covalent bond. Higher values of k₃₃/k₁₁,facilitate, for example, flatter transmission characteristic lines in TNcells with a 90° twist (in order to achieve gray shades) and steepertransmission characteristic lines in STN, SBE and OMI cells (greatermultiplexability), and vice versa.

[0140] The optimum mixing ratio of the compounds of the formulae I, IAand II+III+IV+V+VI depends substantially on the desired properties, onthe choice of the components of the formulae I, IA, II, III, IV, Vand/or VI, and on the choice of any further components that may bepresent. Suitable mixing ratios within the range given above can easilybe determined from case to case.

[0141] The total amount of compounds of the formulae IA and I to XII inthe mixtures according to the invention is not crucial. The mixtures cantherefore comprise one or more further components for the purposes ofoptimization of various properties. However, the observed effect on theaddressing times and the threshold voltage is generally greater, thehigher the total concentration of compounds of the formulae IA and I toXII.

[0142] In a particularly preferred embodiment, the media according tothe invention comprise compounds of the formulae II to VI (preferablyII, IIII and/or IV, in particular IVa) in which X⁰ is F, OCF₃, OCHF₂,OCH═CF₂, OCF═CF₂ or OCF₂-CF₂H. A favorable synergistic effect with thecompounds of the formulae I and IA results in particularly advantageousproperties. In particular, mixtures comprising compounds of the formulaeI and IA and of the formula II are distinguished by their low thresholdvoltages.

[0143] The individual compounds of the formulae IA and I to XVIII andtheir sub-formulae which can be used in the media according to theinvention are either known or can be prepared analogously to the knowncompounds.

[0144] The construction of the MLC display according to the inventionfrom polarizers, electrode base plates and surface-treated electrodescorresponds to the usual design for displays of this type. The termusual design is broadly drawn here and also covers all derivatives andmodifications of the MLC display, in particular including matrix displayelements based on poly-Si TFTs or MIM.

[0145] A significant difference between the displays according to theinvention and the hitherto conventional displays based on the twistednematic cell consists, however, in the choice of the liquid-crystalparameters of the liquid-crystal layer.

[0146] The liquid-crystal mixtures which can be used in accordance withthe invention are prepared in a manner conventional per se. In general,the desired amount of the components used in lesser amount is dissolvedin the components making up the principal constituent, advantageously atelevated temperature. It is also possible to mix solutions of thecomponents in an organic solvent, for example in acetone, chloroform ormethanol, and to remove the solvent again, for example by distillation,after thorough mixing.

[0147] The dielectrics may also comprise further additives known to theperson skilled in the art and described in the literature, such as, forexample, stabilizers, UV filters and antioxidants. For example, 0-15% ofpleochroic dyes or chiral dopants can be added. Suitable stabilizers, UVfilters, antioxidants, etc., are listed below in Table D.

[0148] The entire disclosure of all applications, patents andpublications, cited herein and of corresponding German application No.10309513.6, filed Mar. 5, 2003 is incorporated by reference herein.

[0149] C denotes a crystalline phase, S a smectic phase, S_(c) a smecticC phase, N a nematic phase and I the isotropic phase.

[0150] V₁₀ denotes the voltage for 10% transmission (viewing angleperpendicular to the plate surface). ton denotes the switch-on time andtoff the switch-off time at an operating voltage corresponding to 2.0times the value of V₁₀. An denotes the optical anisotropy. Δε denotesthe dielectric anisotropy (Δε=ε∥−ε⊥, where ε∥ denotes the dielectricconstant parallel to the longitudinal molecular axes and ε⊥ denotes thedielectric constant perpendicular thereto). The electro-optical data aremeasured in a TN cell at the 1st minimum (i.e. at a d·Δn value of 0.5μm) at 20° C., unless expressly stated otherwise. The optical data aremeasured at 20° C., unless expressly stated otherwise.

[0151] In the present application and in the examples below, thestructures of the liquid-crystal compounds are indicated by means ofacronyms, the transformation into chemical formulae taking place inaccordance with Tables A and B below. All radicals C_(n)H_(2n+1) andC_(m)H_(2m+1) are straight-chain alkyl radicals having n and m carbonatoms respectively; n and m are integers and are preferably 0, 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding in Table B is self-evident.In Table A, only the acronym for the parent structure is indicated. Inindividual cases, the acronym for the parent structure is followed,separated by a dash, by a code for the substituents R^(1*), R^(2*),L^(1*) and L^(2*): Code for R¹*, R²*, L¹*, L²* R¹* R²* L¹* L²* nmC_(n)H_(2n+1) C_(m)H_(2m+1) H H nOm OC_(n)H_(2n+1) OC_(m)H_(2m+1) H HnO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) H H n C_(n)H_(2n+1) CN H H nN.FC_(n)H_(2n+1) CN F H nN.F.F C_(n)H_(2n+1) CN F F nF C_(n)H_(2n+1) F H HnOF OC_(n)H_(2n+1) F H H nF.F C_(n)H_(2n+1) F F H nF.F.F C_(n)H_(2n+1) FF F nmF C_(n)H_(2n+1) C_(m)H_(2m+1) F H nOCF₃ C_(n)H_(2n+1) OCF₃ H HnOCF₃.F C_(n)H_(2n+1) OCF₃ F H n-Vm C_(n)H_(2n+1) —CH═CH—C_(m)H_(2m+1) HH nV-Vm C_(n)H_(2n+1)— —CH═CH—C_(m)H_(2m+1) H H CH═CH— nOCF₃.F.FC_(n)H_(2n+1) OCF₃ F F

[0152] Preferred mixture components are given in Tables A and B. TABLE A

[0153] TABLE B

[0154] Particular preference is given to liquid-crystalline mixtureswhich, besides the compounds of the formulae I and IA, comprise at leastone, two, three or four compounds from Table B. TABLE C [0079] Table Cshows possible dopants which can be added to the mixtures according tothe invention. The mixtures according to the invention preferablycomprise 0.01-10% by weight of a dopant or dopant mixture. Of thedopants mentioned, particular preference is given to CN, CM 44,R/S-2011, R/S-4011, R/S-5011, furthermore C15 or CB15.

[0155] TABLE D [0080] Stabilizers which can be added, for example, tothe mixtures according to the invention are mentioned below. If themixtures according to the invention comprise a stabilizer, it is addedin amounts of from 0.01 to 10% by weight.

[0156] The following examples are intended to explain the inventionwithout restricting it. Above and below, percentages are per cent byweight. All temperatures are given in degrees Celsius. m.p. denotesmelting point, cl.p. clearing point. Furthermore, C=crystalline state,N=nematic phase, S=smectic phase and I=isotropic phase. The data betweenthese symbols represent the transition temperatures. An denotes opticalanisotropy (589 nm, 20° C.), Δε the dielectric anisotropy (1 kHz, 20°C). The flow viscosity ν₂₀ (mm²/sec) was determined at 20° C. Therotational viscosity γ₁ (mPa·s) is likewise determined at 20° C.

EXAMPLES Example 1

[0157]

[0158] Step 1.1

[0159] A solution of 0.2 mol of 1 in 300 ml of THF is treated with 0.21mol of lithium diisopropylamide (LDA; 1 M in THF) at −40° C. After 30minutes, a vigorous stream of CO₂ is passed in. The reaction mixture ispoured into 1.5 1 of ice-cold 1 N HCl. The solution is extracted withCH₂Cl₂, and the combined organic extracts are dried over Na₂SO₄ andevaporated to dryness. For purification, the crude product isrecrystallized from toluene. The carboxylic acid obtained in this way isdissolved in 200 ml of SOCl₂ and, after addition of 0.1 ml of DMF,heated at the boil for 3 hours. The excess SOCl₂ is removed bydistillation.

[0160] Step 1.2

[0161] Firstly 0.11 mol of propane-1,3-dithiol, then 0.25 mol oftrifluoromethanesulfonic acid are added to 0.1 mol of 2 at 0° C. Themixture is stirred for 1 hour with ice-cooling, and then 0.4 mol ofacetic anhydride is allowed to run in slowly. After a further hour, 500ml of diethyl ether are added, and the precipitated dithianylium salt 3is filtered off with suction and dried under reduced pressure.

[0162] Step 1.3

[0163] A suspension of 0.1 mol of 3 in 300 ml of CH₂Cl₂ is cooled to−70° C., and a mixture of 0.15 mol of 3,4,5-trifluorophenol, 0.17 mol ofNEt₃ and 100 ml of CH₂Cl₂ is added dropwise. After 5 minutes, firstly0.5 mol of NEt₃·3HF and, after a further 5 minutes, 0.5 mol of Br₂ areadded dropwise. The mixture is stirred at −70° C. for 1 hour, thenallowed to come to room temperature, and the orange-yellow solution ispoured into ice-cold 0.1 N NaOH. The mixture is extracted with CH₂Cl₂,and the combined organic extracts are dried over Na₂SO₄ and evaporatedto dryness in a rotary evaporator. For further purification, the crudeproduct is dissolved in n-heptane and filtered through a silica gelfrit. The product 4 is subsequently recrystallized from n-heptane at−20° C.

[0164] Step 1.4

[0165] A suspension of 0.1 mol of 3 in 300 ml of CH₂Cl₂ is cooled to−70° C., and a mixture of 0.15 mol of3,5-difluoro-4-trifluoromethoxyphenol, 0.17 mol of NEt₃ and 100 ml ofCH₂Cl₂ is added dropwise. After 5 minutes, firstly 0.5 mol of NEt₃·3HFand, after a further 5 minutes, 0.5 mol of Br₂ are added dropwise. Themixture is stirred at −70° C. for 1 hour, then allowed to come to roomtemperature, and the orange-yellow solution is poured into ice-cold 0.1N NaOH. The mixture is extracted with CH₂Cl₂, and the combined organicextracts are dried over Na₂SO₄ and evaporated to dryness in a rotaryevaporator. For further purification, the crude product is dissolved inn-heptane and filtered through a silica gel frit. The product 5 issubsequently recrystallized from n-heptane at −20° C.

[0166] General procedure for 7a-f: A mixture of 50 mmol of 6a-c, 50 mmolof 4 or 5, 2.5 mmol of Pd(PPh₃)₄, 300 ml of toluene and 300 ml of Naborate buffer pH 9 is stirred at 80° C. for 18 hours. The mixture ispoured into 500 ml of 0.1 N HCl, and the product is extracted withCH₂Cl₂, dried over Na₂SO₄ and evaporated to dryness in a rotaryevaporator. The crude product is chromatographed over silica gel inn-heptane and subsequently recrystallized from n-heptane at −20° C.

[0167] The following compounds of the formula

[0168] are prepared analogously: R² L⁷ L⁸ X² L³ L⁴ H H H F H H H H H F FH C 88 I; Δn = 0.1231; H H H F F F Δε = 22.4 C 91 I; Δn = 0.0991; H H FF F F Δε = 23.8 H F F F F F CH₃ H H F H H CH₃ H H F F H CH₃ H H F F FCH₃ H F F F F CH₃ F F F F F C₂H₅ H H F H H C₂H₅ H H F F H C₂H₅ H H F F FC₂H₅ H F F F F C 85 N (85.0) I; C₂H₅ F F F F F Δn = 0.1150; Δε = 28.7n-C₃H₇ H H F H H n-C₃H₇ H H F F H n-C₃H₇ H H F F F n-C₃H₇ H F F F F C 94N 112.4 I; n-C₃H₇ F F F F F Δn = 0.1240; Δε = 28.6 n-C₄H₉ H H F H Hn-C₄H₉ H H F F H n-C₄H₉ H H F F F n-C₄H₉ H F F F F n-C₄H₉ F F F F Fn-C₅H₁₁ H H F H H n-C₅H₁₁ H H F F H n-C₅H₁₁ H H F F F n-C₅H₁₁ H F F F Fn-C₅H₁₁ F F F F F n-C₆H₁₃ H H F H H n-C₆H₁₃ H H F F H n-C₆H₁₃ H H F F Fn-C₆H₁₃ H F F F F n-C₆H₁₃ F F F F F CH₂═CH H H F H H CH₂═CH H H F F HCH₂═CH H H F F F CH₂═CH H F F F F CH₂═CH F F F F F CH₃CH═CH H H F H HCH₃CH═CH H H F F H CH₃CH═CH H H F F F CH₃CH═CH H F F F F CH₃CH═CH F F FF F CH₂═CHCH₂CH₂ H H F H H CH₂═CHCH₂CH₂ H H F F H CH₂═CHCH₂CH₂ H H F F FCH₂═CHCH₂CH₂ H F F F F CH₂═CHCH₂CH₂ F F F F F H H H OCF₃ H H H H H OCF₃F H C 69 I; Δn = 0.1246; H H H OCF₃ F F Δε = 28.2 H H F OCF₃ F F H F FOCF₃ F F CH₃ H H OCF₃ H H CH₃ H H OCF₃ F H CH₃ H H OCF₃ F F CH₃ H F OCF₃F F CH₃ F F OCF₃ F F C₂H₅ H H OCF₃ H H C₂H₅ H H OCF₃ F H C₂H₅ H H OCF₃ FF C 76 N 120.7 I; C₂H₅ H F OCF₃ F F Δn = 0.1295; Δε = 26.9 C 77 N 103.5I; C₂H₅ F F OCF₃ F F Δn = 0.1154; Δε = 30.5 n-C₃H₇ H H OCF₃ H H n-C₃H₇ HH OCF₃ F H n-C₃H₇ H H OCF₃ F F C 71 N 142.5 I; n-C₃H₇ H F OCF₃ F F Δn =0.1320; Δε = 26.8 C 77 N 128.7 I; n-C₃H₇ F F OCF₃ F F Δn = 0.1240; Δε =29.9 n-C₄H₉ H H OCF₃ H H n-C₄H₉ H H OCF₃ F H n-C₄H₉ H H OCF₃ F F n-C₄H₉H F OCF₃ F F n-C₄H₉ F F OCF₃ F F n-C₅H₁₁ H H OCF₃ H H n-C₅H₁₁ H H OCF₃ FH n-C₅H₁₁ H H OCF₃ F F n-C₅H₁₁ H F OCF₃ F F n-C₅H₁₁ F F OCF₃ F F n-C₆H₁₃H H OCF₃ H H n-C₆H₁₃ H H OCF₃ F H n-C₆H₁₃ H H OCF₃ F F n-C₆H₁₃ H F OCF₃F F n-C₆H₁₃ F F OCF₃ F F CH₂═CH H H OCF₃ H H CH₂═CH H H OCF₃ F H CH₂═CHH H OCF₃ F F CH₂═CH H F OCF₃ F F CH₂═CH F F OCF₃ F F CH₃CH═CH H H OCF₃ HH CH₃CH═CH H H OCF₃ F H CH₃CH═CH H H OCF₃ F F CH₃CH═CH H F OCF₃ F FCH₃CH═CH F F OCF₃ F F CH₂═CHCH₂CH₂ H H OCF₃ H H CH₂═CHCH₂CH₂ H H OCF₃ FH CH₂═CHCH₂CH₂ H H OCF₃ F F CH₂═CHCH₂CH₂ H F OCF₃ F F CH₂═CHCH₂CH₂ F FOCF₃ F F H H H Cl H H H H H Cl F H H H H Cl F F C 92 I; Δn = 0.1489; Δε= 20.4 H H H Cl H H H H H Cl F H H H H Cl F F H H F Cl F F H F F Cl F FCH₃ H H Cl H H CH₃ H H Cl F H CH₃ H H Cl F F CH₃ H F Cl F F CH₃ F F Cl FF C₂H₅ H H Cl H H C₂H₅ H H Cl F H C₂H₅ H H Cl F F C₂H₅ H F Cl F F C₂H₅ FF Cl F F n-C₃H₇ H H Cl H H n-C₃H₇ H H Cl F H n-C₃H₇ H H Cl F F n-C₃H₇ HF Cl F F n-C₃H₇ F F Cl F F n-C₄H₉ H H Cl H H n-C₄H₉ H H Cl F H n-C₄H₉ HH Cl F F n-C₄H₉ H F Cl F F n-C₄H₉ F F Cl F F n-C₅H₁₁ H H Cl H H n-C₅H₁₁H H Cl F H n-C₅H₁₁ H H Cl F F n-C₅H₁₁ H F Cl F F n-C₅H₁₁ F F Cl F Fn-C₆H₁₃ H H Cl H H n-C₆H₁₃ H H Cl F H n-C₆H₁₃ H H Cl F F n-C₆H₁₃ H F ClF F n-C₆H₁₃ F F Cl F F CH₂═CH H H Cl H H CH₂═CH H H Cl F H CH₂═CH H H ClF F CH₂═CH H F Cl F F CH₂═CH F F Cl F F CH₃CH═CH H H Cl H H CH₃CH═CH H HCl F H CH₃CH═CH H H Cl F F CH₃CH═CH H F Cl F F CH₃CH═CH F F Cl F FCH₂═CHCH₂CH₂ H H Cl H H CH₂═CHCH₂CH₂ H H Cl F H CH₂═CHCH₂CH₂ H H Cl F FCH₂═CHCH₂CH₂ H F Cl F F CH₂═CHCH₂CH₂ F F Cl F F H H H OCHF₂ H H H H HOCHF₂ F H H H H OCHF₂ F F H H F OCHF₂ F F H F F OCHF₂ F F CH₃ H H OCHF₂H H CH₃ H H OCHF₂ F H CH₃ H H OCHF₂ F F CH₃ H F OCHF₂ F F CH₃ F F OCHF₂F F C₂H₅ H H OCHF₂ H H C₂H₅ H H OCHF₂ F H C₂H₅ H H OCHF₂ F F C₂H₅ H FOCHF₂ F F C₂H₅ F F OCHF₂ F F n-C₃H₇ H H OCHF₂ H H n-C₃H₇ H H OCHF₂ F Hn-C₃H₇ H H OCHF₂ F F n-C₃H₇ H F OCHF₂ F F n-C₃H₇ F F OCHF₂ F F n-C₄H₉ HH OCHF₂ H H n-C₄H₉ H H OCHF₂ F H n-C₄H₉ H H OCHF₂ F F n-C₄H₉ H F OCHF₂ FF n-C₄H₉ F F OCHF₂ F F n-C₅H₁₁ H H OCHF₂ H H n-C₅H₁₁ H H OCHF₂ F Hn-C₅H₁₁ H H OCHF₂ F F n-C₅H₁₁ H F OCHF₂ F F n-C₅H₁₁ F F OCHF₂ F Fn-C₆H₁₃ H H OCHF₂ H H n-C₆H₁₃ H H OCHF₂ F H n-C₆H₁₃ H H OCHF₂ F Fn-C₆H₁₃ H F OCHF₂ F F n-C₆H₁₃ F F OCHF₂ F F CH₂═CH H H OCHF₂ H H CH₂═CHH H OCHF₂ F H CH₂═CH H H OCHF₂ F F CH₂═CH H F OCHF₂ F F CH₂═CH F F OCHF₂F F CH₃CH═CH H H OCHF₂ H H CH₃CH═CH H H OCHF₂ F H CH₃CH═CH H H OCHF₂ F FCH₃CH═CH H F OCHF₂ F F CH₃CH═CH F F OCHF₂ F F CH₂═CHCH₂CH₂ H H OCHF₂ H HCH₂═CHCH₂CH₂ H H OCHF₂ F H CH₂═CHCH₂CH₂ H H OCHF₂ F F CH₂═CHCH₂CH₂ H FOCHF₂ F F CH₂═CHCH₂CH₂ F F OCHF₂ F F H H H SF₅ H H H H H SF₅ F H H H HSF₅ F F H H F SF₅ F F H F F SF₅ F F CH₃ H H SF₅ H H CH₃ H H SF₅ F H CH₃H H SF₅ F F CH₃ H F SF₅ F F CH₃ F F SF₅ F F C₂H₅ H H SF₅ H H C₂H₅ H HSF₅ F H C₂H₅ H H SF₅ F F C₂H₅ H F SF₅ F F C₂H₅ F F SF₅ F F n-C₃H₇ H HSF₅ H H n-C₃H₇ H H SF₅ F H n-C₃H₇ H H SF₅ F F n-C₃H₇ H F SF₅ F F n-C₃H₇F F SF₅ F F n-C₄H₉ H H SF₅ H H n-C₄H₉ H H SF₅ F H n-C₄H₉ H H SF₅ F Fn-C₄H₉ H F SF₅ F F n-C₄H₉ F F SF₅ F F n-C₅H₁₁ H H SF₅ H H n-C₅H₁₁ H HSF₅ F H n-C₅H₁₁ H H SF₅ F F n-C₅H₁₁ H F SF₅ F F n-C₅H₁₁ F F SF₅ F Fn-C₆H₁₃ H H SF₅ H H n-C₆H₁₃ H H SF₅ F H n-C₆H₁₃ H H SF₅ F F n-C₆H₁₃ H FSF₅ F F n-C₆H₁₃ F F SF₅ F F CH₂═CH H H SF₅ H H CH₂═CH H H SF₅ F H CH₂═CHH H SF₅ F F CH₂═CH H F SF₅ F F CH₂═CH F F SF₅ F F CH₃CH═CH H H SF₅ H HCH₃CH═CH H H SF₅ F H CH₃CH═CH H H SF₅ F F CH₃CH═CH H F SF₅ F F CH₃CH═CHF F SF₅ F F CH₂═CHCH₂CH₂ H H SF₅ H H CH₂═CHCH₂CH₂ H H SF₅ F HCH₂═CHCH₂CH₂ H H SF₅ F F CH₂═CHCH₂CH₂ H F SF₅ F F CH₂═CHCH₂CH₂ F F SF₅ FF H H H OC₃F₇ H H H H H OC₃F₇ F H H H H OC₃F₇ F F H H F OC₃F₇ F F H F FOC₃F₇ F F CH₃ H H OC₃F₇ H H CH₃ H H OC₃F₇ F H CH₃ H H OC₃F₇ F F CH₃ H FOC₃F₇ F F CH₃ F F OC₃F₇ F F C₂H₅ H H OC₃F₇ H H C₂H₅ H H OC₃F₇ F H C₂H₅ HH OC₃F₇ F F C₂H₅ H F OC₃F₇ F F C₂H₅ F F OC₃F₇ F F n-C₃H₇ H H OC₃F₇ H Hn-C₃H₇ H H OC₃F₇ F H n-C₃H₇ H H OC₃F₇ F F n-C₃H₇ H F OC₃F₇ F F n-C₃H₇ FF OC₃F₇ F F n-C₄H₉ H H OC₃F₇ H H n-C₄H₉ H H OC₃F₇ F H n-C₄H₉ H H OC₃F₇ FF n-C₄H₉ H F OC₃F₇ F F n-C₄H₉ F F OC₃F₇ F F n-C₅H₁₁ H H OC₃F₇ H Hn-C₅H₁₁ H H OC₃F₇ F H n-C₅H₁₁ H H OC₃F₇ F F n-C₅H₁₁ H F OC₃F₇ F Fn-C₅H₁₁ F F OC₃F₇ F F n-C₆H₁₃ H H OC₃F₇ H H n-C₆H₁₃ H H OC₃F₇ F Hn-C₆H₁₃ H H OC₃F₇ F F n-C₆H₁₃ H F OC₃F₇ F F n-C₆H₁₃ F F OC₃F₇ F F CH₂═CHH H OC₃F₇ H H CH₂═CH H H OC₃F₇ F H CH₂═CH H H OC₃F₇ F F CH₂═CH H F OC₃F₇F F CH₂═CH F F OC₃F₇ F F CH₃CH═CH H H OC₃F₇ H H CH₃CH═CH H H OC₃F₇ F HCH₃CH═CH H H OC₃F₇ F F CH₃CH═CH H F OC₃F₇ F F CH₃CH═CH F F OC₃F₇ F FCH₂═CHCH₂CH₂ H H OC₃F₇ H H CH₂═CHCH₂CH₂ H H OC₃F₇ F H CH₂═CHCH₂CH₂ H HOC₃F₇ F F CH₂═CHCH₂CH₂ H F OC₃F₇ F F CH₂═CHCH₂CH₂ F F OC₃F₇ F F H H HOCHFCF₃ H H H H H OCHFCF₃ F H H H H OCHFCF₃ F F H H F OCHFCF₃ F F H F FOCHFCF₃ F F CH₃ H H OCHFCF₃ H H CH₃ H H OCHFCF₃ F H CH₃ H H OCHFCF₃ F FCH₃ H F OCHFCF₃ F F CH₃ F F OCHFCF₃ F F C₂H₅ H H OCHFCF₃ H H C₂H₅ H HOCHFCF₃ F H C₂H₅ H H OCHFCF₃ F F C₂H₅ H F OCHFCF₃ F F C₂H₅ F F OCHFCF₃ FF n-C₃H₇ H H OCHFCF₃ H H n-C₃H₇ H H OCHFCF₃ F H n-C₃H₇ H H OCHFCF₃ F Fn-C₃H₇ H F OCHFCF₃ F F n-C₃H₇ F F OCHFCF₃ F F n-C₄H₉ H H OCHFCF₃ H Hn-C₄H₉ H H OCHFCF₃ F H n-C₄H₉ H H OCHFCF₃ F F n-C₄H₉ H F OCHFCF₃ F Fn-C₄H₉ F F OCHFCF₃ F F n-C₅H₁₁ H H OCHFCF₃ H H n-C₅H₁₁ H H OCHFCF₃ F Hn-C₅H₁₁ H H OCHFCF₃ F F n-C₅H₁₁ H F OCHFCF₃ F F n-C₅H₁₁ F F OCHFCF₃ F Fn-C₆H₁₃ H H OCHFCF₃ H H n-C₆H₁₃ H H OCHFCF₃ F H n-C₆H₁₃ H H OCHFCF₃ F Fn-C₆H₁₃ H F OCHFCF₃ F F n-C₆H₁₃ F F OCHFCF₃ F F CH₂═CH H H OCHFCF₃ H HCH₂═CH H H OCHFCF₃ F H CH₂═CH H H OCHFCF₃ F F CH₂═CH H F OCHFCF₃ F FCH₂═CH F F OCHFCF₃ F F CH₃CH═CH H H OCHFCF₃ H H CH₃CH═CH H H OCHFCF₃ F HCH₃CH═CH H H OCHFCF₃ F F CH₃CH═CH H F OCHFCF₃ F F CH₃CH═CH F F OCHFCF₃ FF CH₂═CHCH₂CH₂ H H OCHFCF₃ H H CH₂═CHCH₂CH₂ H H OCHFCF₃ F H CH₂═CHCH₂CH₂H H OCHFCF₃ F F CH₂═CHCH₂CH₂ H F OCHFCF₃ F F CH₂═CHCH₂CH₂ F F OCHFCF₃ FF H H H OCF₂CHFCF₃ H H H H H OCF₂CHFCF₃ F H H H H OCF₂CHFCF₃ F F H H FOCF₂CHFCF₃ F F H F F OCF₂CHFCF₃ F F CH₃ H H OCF₂CHFCF₃ H H CH₃ H HOCF₂CHFCF₃ F H CH₃ H H OCF₂CHFCF₃ F F CH₃ H F OCF₂CHFCF₃ F F CH₃ F FOCF₂CHFCF₃ F F C₂H₅ H H OCF₂CHFCF₃ H H C₂H₅ H H OCF₂CHFCF₃ F H C₂H₅ H HOCF₂CHFCF₃ F F C₂H₅ H F OCF₂CHFCF₃ F F C₂H₅ F F OCF₂CHFCF₃ F F n-C₃H₇ HH OCF₂CHFCF₃ H H n-C₃H₇ H H OCF₂CHFCF₃ F H n-C₃H₇ H H OCF₂CHFCF₃ F Fn-C₃H₇ H F OCF₂CHFCF₃ F F n-C₃H₇ F F OCF₂CHFCF₃ F F n-C₄H₉ H HOCF₂CHFCF₃ H H n-C₄H₉ H H OCF₂CHFCF₃ F H n-C₄H₉ H H OCF₂CHFCF₃ F Fn-C₄H₉ H F OCF₂CHFCF₃ F F n-C₄H₉ F F OCF₂CHFCF₃ F F n-C₅H₁₁ H HOCF₂CHFCF₃ H H n-C₅H₁₁ H H OCF₂CHFCF₃ F H n-C₅H₁₁ H H OCF₂CHFCF₃ F Fn-C₅H₁₁ H F OCF₂CHFCF₃ F F n-C₅H₁₁ F F OCF₂CHFCF₃ F F n-C₆H₁₃ H HOCF₂CHFCF₃ H H n-C₆H₁₃ H H OCF₂CHFCF₃ F H n-C₆H₁₃ H H OCF₂CHFCF₃ F Fn-C₆H₁₃ H F OCF₂CHFCF₃ F F n-C₆H₁₃ F F OCF₂CHFCF₃ F F CH₂═CH H HOCF₂CHFCF₃ H H CH₂═CH H H OCF₂CHFCF₃ F H CH₂═CH H H OCF₂CHFCF₃ F FCH₂═CH H F OCF₂CHFCF₃ F F CH₂═CH F F OCF₂CHFCF₃ F F CH₃CH═CH H HOCF₂CHFCF₃ H H CH₃CH═CH H H OCF₂CHFCF₃ F H CH₃CH═CH H H OCF₂CHFCF₃ F FCH₃CH═CH H F OCF₂CHFCF₃ F F CH₃CH═CH F F OCF₂CHFCF₃ F F CH₂═CHCH₂CH₂ H HOCF₂CHFCF₃ H H CH₂═CHCH₂CH₂ H H OCF₂CHFCF₃ F H CH₂═CHCH₂CH₂ H HOCF₂CHFCF₃ F F CH₂═CHCH₂CH₂ H F OCF₂CHFCF₃ F F CH₂═CHCH₂CH₂ F FOCF₂CHFCF₃ F F H H H CN H H H H H CN F H H H H CN F F H H F CN F F H F FCN F F CH₃ H H CN H H CH₃ H H CN F H CH₃ H H CN F F CH₃ H F CN F F CH₃ FF CN F F C₂H₅ H H CN H H C₂H₅ H H CN F H C₂H₅ H H CN F F C₂H₅ H F CN F FC₂H₅ F F CN F F n-C₃H₇ H H CN H H n-C₃H₇ H H CN F H n-C₃H₇ H H CN F Fn-C₃H₇ H F CN F F n-C₃H₇ F F CN F F n-C₄H₉ H H CN H H n-C₄H₉ H H CN F Hn-C₄H₉ H H CN F F n-C₄H₉ H F CN F F n-C₄H₉ F F CN F F n-C₅H₁₁ H H CN H Hn-C₅H₁₁ H H CN F H n-C₅H₁₁ H H CN F F n-C₅H₁₁ H F CN F F n-C₅H₁₁ F F CNF F n-C₆H₁₃ H H CN H H n-C₆H₁₃ H H CN F H n-C₆H₁₃ H H CN F F n-C₆H₁₃ H FCN F F n-C₆H₁₃ F F CN F F CH₂═CH H H CN H H CH₂═CH H H CN F H CH₂═CH H HCN F F CH₂═CH H F CN F F CH₂═CH F F CN F F CH₃CH═CH H H CN H H CH₃CH═CHH H CN F H CH₃CH═CH H H CN F F CH₃CH═CH H F CN F F CH₃CH═CH F F CN F FCH₂═CHCH₂CH₂ H H CN H H CH₂═CHCH₂CH₂ H H CN F H CH₂═CHCH₂CH₂ H H CN F FCH₂═CHCH₂CH₂ H F CN F F CH₂═CHCH₂CH₂ F F CN F F

Example M1

[0169] CCP-1F.F.F 2.00% Clearing point [° C.]: 72.0 CCP-3OCF₃ 5.00% Δn[589 nm; 20° C.]: 0.0779 CCQU-5-F 4.00% γ₁ [mPa · s; 20° C.]: 98CCQU-1-F 14.00%  V₁₀ [V]: 1.23 CCQU-2-F 9.00% CCQU-3-F 9.00% CPUQU-2-F8.00% CPUQU-3-F 3.00% CDU-2-F 8.00% CDU-3-F 9.00% PGU-2-F 4.00% CC-3-V112.00%  CC-5-V 8.00% CCH-35 5.00%

Example M2

[0170] CC-3-V 19.00% Clearing point [° C.]: 80.6 CCH-35 4.00% Δn [589nm; 20° C.]: 0.0763 CCQU-1-F 11.00% γ₁ [mPa · s; 20° C.]: 105 CCQU-2-F10.00% V₁₀ [V]: 1.24 CCP-2OCF₃ 8.00% CCP-3OCF₃ 8.00% CCP-4OCF₃ 6.00%CCZU-2-F 4.00% CCZU-3-F 15.00% CGUQU-2-F 10.00% CGUQU-3-F 5.00%

Example M3

[0171] CCP-1F.F.F 8.00% Clearing point [° C.]: 90.5 CCP-2F.F.F 8.00% Δn[589 nm; 20° C.]: 0.0783 CCP-3F.F.F 7.00% V₁₀ [V]: 1.14 CCP-5F.F.F 5.00%CCP-20CF₃.F 10.00% CCP-50CF₃.F 10.00% CGUQU-2-F 6.00% CGUQU-3-F 5.00%CCOC-3-3 3.00% CCOC-4-3 4.00% CCOC-3-5 2.00% CCQU-1-F 10.00% CCQU-2-F10.00% CCQU-3-F 12.00%

Example M4

[0172] CCP-1F.F.F 8.00% CCP-2F.F.F 9.00% CCP-3F.F.F 9.00% CCP-5F.F.F5.00% CCP-20CF₃.F 11.00% CCP-50CF₃.F 12.00% CCQU-2-F 10.00% CCQU-3-F12.00% CCQU-5-F 8.00% CUUQU-2-F 5.00% CUUQU-3-F 6.00% CCH-5CF₃ 1.00%CCOC-3-3 2.00% CCOC-4-3 2.00%

Example M5

[0173] CECU-2-F 4.00% Clearing point [° C.]: 79.1 CECU-5-F 9.00% Δn [589nm; 20° C.]: 0.0742 CCP-2F.F.F 9.00% Δε [kHz, 20° C.]: 11.1 CCP-3F.F.F10.00% γ₁ [mPa · s; 20° C.]: 163 CCP-5F.F.F 6.00% CCZU-2-F 4.00%CCZU-3-F 15.00% CCZU-5-F 4.00% CCPU-5-F 2.00% CCQU-1-F 8.00% CCQU-2-F10.00% CCQU-3-F 11.00% CGUQU-2-F 8.00%

Example M6

[0174] CCQG-2-F 8.00% Clearing point [° C.]: 73.5 CCQG-3-F 8.00% Δn [589nm; 20° C.]: 0.0733 CCQG-5-F 8.00% Δε [kHz, 20° C.]: 11.8 CGUQU-2-F7.00% γ₁ [mPa · s; 20° C.]: 138 CGUQU-3-F 5.00% CCQU-1-F 9.00% CCQU-2-F10.00% CCQU-3-F 10.00% CCQU-2-OT 9.00% CCQU-3-OT 9.00% CCQU-4-OT 9.00%CQU-3-F 4.00% CQU-5-F 4.00%

[0175] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0176] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A liquid-crystalline medium comprising a mixture of polar compoundsof positive dielectric anisotropy, which comprises one or more compoundsof the formula I

and one or more compounds of the formula IA

in which the individual radicals have the following meanings: R¹ and R²are each, independently of one another, H, a halogenated orunsubstituted alkyl radical having from 1 to 15 carbon atoms, where oneor more CH₂ groups in these radicals are optionally replaced, in eachcase independently of one another, by —C≡C—, —CH═CH—, —O—,

 —CO—O— or —O—CO— in such a way that O atoms are not linked directly toone another, X¹ and X² are each, independently of one another, F, Cl,CN, SF₅, SCN, OCN, or NCS, or a halogenated alkyl radical, a halogenatedalkenyl radical, a halogenated alkoxy radical or a halogenatedalkenyloxy radical each having 1 to 6 carbon atoms,

Z¹ is —CH₂CH₂—, —CH═CH—, —C≡C—, —COO—, —CH₂O—, —OCH₂—, —OOC—, —(CH₂)₄—,—CHFO—, —CH═CF—, —CF═CH—, —CF═CF—, —C₂F₄—, —CF₂O—, —OCF₂— or a singlebond, L¹⁻⁸ are each, independently of one another, H or F.
 2. Aliquid-crystalline medium according to claim 1, which comprises one, twoor more compounds of the formulae IA-1 to IA-108:

in which R² is as defined above.
 3. A liquid-crystalline mediumaccording to claim 1, which comprises one or more compounds of theformulae I-1 to I-27:

in which R¹ is as defined above.
 4. A liquid-crystalline mediumaccording to claim 2, which comprises one or more compounds of theformulae I-1 to I-27:


5. A liquid-crystalline medium according to claim 1, which additionallycomprises one or more compounds selected from the group consisting ofcompounds of the formulae II, III, IV, V and VI:

in which the individual radicals have the following meanings: R⁰ is H,n-alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl, each having 1 to 9carbon atoms, X⁰ is F, Cl, halogenated alkyl, halogenated alkenyl,halogenated alkenyloxy or alkoxy having 1 to 6 carbon atoms, Z⁰ is—C₂F₄—, —CF═CF—, —CH═CF—, —CF═CH—, —C₂H₄—, —(CH₂)₄—, —OCHF—, —CHFO—,—CH═CH—, —COO—, —OCO—, —CF₂O—, —OCF₂—, —OCH₂— or —CH₂O—, Y¹ and Y² areeach, independently of one another, H or F, r is 0 or 1, and thecompound of the formula VI is not identical with the compound of theformula I.
 6. A liquid-crystalline medium according to claim 4, whichadditionally comprises one or more compounds selected from the groupconsisting of compounds of the formulae II, III, IV, V and VI:

in which the individual radicals have the following meanings: R⁰ is H,n-alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl, each having 1 to 9carbon atoms, X⁰ is F, Cl, halogenated alkyl, halogenated alkenyl,halogenated alkenyloxy or alkoxy having 1 to 6 carbon atoms, Z⁰ is—C₂F₄—, —CF═CF—, —CH═CF—, —CF═CH—, —C₂H₄—, —(CH₂)₄—, —OCHF—, —CHFO—,—CH═CH—, —COO—, —OCO—, —CF₂O—, —OCF₂—, —OCH₂— or —CH₂O—, Y¹ and Y² areeach, independently of one another, H or F, r is 0 or 1, and thecompound of the formula VI is not identical with the compound of theformula I.
 7. A liquid-crystalline medium according to claim 6, whereinthe proportion of compounds of the formulae IA and I to VI together inthe medium as a whole is at least 50% by weight.
 8. A liquid-crystallinemedium according to claim 1, which additionally comprises one or morecompounds of the formulae Ea to Ef:

in which R⁰ is H, n-alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl,each having 1 to 9 carbon atoms.
 9. A liquid-crystalline mediumaccording to claim 1, which additionally comprises one or more compoundsof the formulae IIa to IIg:

in which R⁰ is H, n-alkyl, oxaalkyl, alkoxy, fluoroalkyl or alkenyl,each having 1 to 9 carbon atoms.
 10. A liquid-crystalline mediumaccording to claim 1, which additionally comprises one or more compoundsof the formulae RI to RIX:

in which R⁰ is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyloxy oralkenyl, each having 1 to 9 carbon atoms, Y¹ is H or F, alkyl and alkyl*are each, independently of one another, a straight-chain or branchedalkyl radical having 1-9 carbon atoms, alkenyl and alkenyl* are each,independently of one another, a straight-chain or branched alkenylradical having from 2 to 9 carbon atoms.
 11. A liquid-crystalline mediumaccording to claim 1, wherein the proportion of compounds of the formulaIA in the medium as a whole is from 5 to 40% by weight.
 12. Aliquid-crystalline medium according to claim 1, wherein the proportionof compounds of the formula I in the medium as a whole is from 5 to 40%by weight.
 13. An electro-optical liquid-crystal display containing aliquid-crystalline medium according to claim 1.